Ive never worked with house-paints before, but I have worked with laquers on older cars. Even the cheaper laquer paint, you can hand-polish them out close to a mirror finish. But what I hate about this, every spec of dust shows. Every minor scratch, any area of paint not *perfectly* level shows up. I almost prefer a gloss white now, simply because you can get fingerprints all over, get it dusty/dirty... no one will notice.
To see what I mean, take a long cheap mirror if you have one, lay it on the table. Under the ceter of it, place something like a pencil/pen, or a wooden ruler. Hold down on one end, and push down on the other slightly. Even a millameter or two of twist or bending, really shows up.
That being said, MDF is even easier than fresh sheet metal, to get a good mirror-finish on. MDF is thick, and its not going to warp/twist/flex on its own while you handle it and build things with it. MDF is already as smooth and glass starting out, its simply a matter of properly applying many coats of paint, wetsanding, and polishing. Try it out, you can even get a damn nice finish with $0.94 cans of gloss spray-paint. Get some 800, 1000, and possibly 2000 grit sandpaper. FYI, 1000 grit sandpaper, the particles on it are supposed to be about as small as smoke. Even without wetsanding or polishing, properly applied paint should give a fairly adequate reflection.
Habs4life, you may want to take pictures along the way showing what/how you did things, and how it turned out in the end. Im sure many other members are wondering exactly how to go about doing this, a DIY/How-to guide from a newbies perspective would be an interesting read.